1. Field of the Invention
The present invention relates to a method and an apparatus for core alignment between optical components to align a pair of optical components (including discrete components and so-called optical modules being composed of a plurality of components).
2. Related Background Art
In general, high precision is required for alignment between a pair of optical components.
For example, a core diameter of a single-mode optical fiber for use in optical communications is in a range from about 3 to 8 μmφ. Meanwhile, focus spot sizes of a semiconductor laser which is a light source and of a condenser lens are also extremely small that the diameter is several micrometers. Accordingly, high precision is required for the core alignment between these optical components. Usually, when light from a semiconductor laser is optically coupled to a single-mode optical fiber, margins of errors to suppress a coupling loss down to −0.5 dB or thereabout are: approximately ±1 μm in a perpendicular direction to an optical axis; approximately ±10 μm in a horizontal direction; and approximately ±0.5° in terms of angular deviation.
In the meantime, the same degree of precision is also required for the core alignments between a semiconductor laser and a waveguide and between an optical fiber and a waveguide.
Conventionally, the core alignment of optical components has been performed as follows: detecting light emitted from a first optical component and introduced to a second optical component with a photodetector; amplifying an output of this photodetector with amplification means; and adjusting relative positions between the first and second optical components based on the output of the amplification means. Various methods of the core alignment, which include the technologies described later, have been proposed. However, a linear amplifier is used as the amplification means for any of the conventional methods of the core alignment.
In a typical conventional method of the core alignment, a tip of an optical fiber is scanned relative to a focus spot of a semiconductor laser by use of an XYZ stage to serially trace a position of a stronger signal. As a method for achieving such a scan in a short period of time, there is a typical method including the steps of: performing spiral scanning to detect a range where given signal intensity is obtained; and finding an optimum point after detection of the range by stepwise two-dimensional or three-dimensional scanning called a hill-climbing method.
Meanwhile, Japanese Patent Application Laid-Open No. 6-265759 (Japanese Patent Publication No.7(1995)-113694) discloses an automatic optical axis alignment apparatus for automatically aligning a pair of optical fibers by: circulating a tip of an optical fiber by use of a piezoactuator designed to scan along a direction displaced by 90°; and detecting a shift of an optical axis in terms of two X and Y directions by phase detection.